The present invention relates generally to treatment of fibrillation by discharge of electrical energy in the region of the heart for converting the dysrhythmia to sinus rhythm, and more particularly to monitoring and treatment of rhythm disorders, primarily atrial but also ventricular, using an external defibrillator in conjunction with a temporary or permanent implanted catheter.
Greater human longevity has resulted in significant increases in the number of cases of atrial fibrillation, and to an extent ventricular fibrillation, particularly in the industrial nations. Atrial fibrillation is one of the primary causes of hospitalization for cardiac rhythm disorders in the United States, and an underlying cause of events of cerebrovascular stroke. Proper and timely treatment and cardioversion of atrial fibrillation would noticeably enhance expectancy and quality of life, and reduce hemodynamic and thromboembolic complications. Anti-arrhythmic drugs have not been effective to measurably reduce the incidence of atrial fibrillation, and have undesirable side effects.
Application of external shocks with energies of between 100 and 350 joules is one therapy for treating atrial fibrillation, but it, too, has a number of risks and complications. Among them are late ventricular fibrillation, pericarditis attributable to the high electrical current, and spinal and other skeletal fractures arising from severe muscular contractions during application of the high energy shock(s).
The art of implanted atrial defibrillation electrodes using lower energies is well developed, as indicated for example by the disclosure of U.S. Pat. No. 5,282,837 to J. Adams et al. The '837 patent describes the discharge of defibrillating energy from an implanted defibrillator, between two electrodes of an implanted catheter threaded through the coronary sinus. Energy discharge electrodes of the catheter are positioned beneath the left atrium near the left ventricle and in a region adjacent the right atrium coronary sinus ostium to minimize the potential for ventricular fibrillation. The implanted defibrillator senses arrhythmia and controls the energy discharge.
Ventricular fibrillation is also arrested with implanted systems as disclosed by Shulte et al in U.S. Pat. No. 5,269,319. In the '319 patent disclosure, two defibrillation electrodes on a single catheter are inserted via the superior vena cava into the right atrium and right ventricular cavity respectively. R-waves are detected and defibrillation impulse energy is synchronized therewith.
It is a principal aim of the present invention to provide improved treatment of atrial fibrillation, and to an extent, ventricular fibrillation.
Another aim of the invention is to significantly reduce the amount of energy required for treatment of atrial fibrillation from external impulse generators, by means of a hybrid system of internal defibrillating electrodes powered by external energy and control means.
Additional problems exist with implanting prior art electrodes and delivery of sufficient energy for defibrillation. Permanently implanted systems are of questionable value if only used for treating atrial fibrillation. In general, effective electrodes employed in the past have required large electrode surface areas to handle high energy impulses, and are thus substantially intrusive. Implantation of netting, barbs and other forms of electrodes or electrode anchoring on or in the vicinity of the heart has also presented a number of problems, and have not been entirely feasible for use with a temporary defibrillation system.
Conditions such as the potential for congestive heart failure can require continuous monitoring after defibrillation rather than or in addition to mere isolated shock treatment. Furthermore, cardiac surgery may call for post-operative monitoring for atrial dysrhythmias, and the delivery of instantaneous treatment when atrial fibrillation is detected.
Accordingly, it is a further object of the invention to provide a method and associated instrumentation for relatively brief periods during hospitalization or clinical study, for example, of continuous monitoring and instantaneous treatment of dysrhythmias, particularly atrial fibrillation, with moderate energy shocks of adequate electrical field gradient to defibrillate when necessary, and with a need only to implant a catheter or lead for delivery of electrical energy to the appropriate region(s) of the heart.